A process for the fluid catalytic cracking of heavy fraction oils

Abstract: A process for the fluid catalytic cracking of heavy fraction oils containing heavy metals such as Ni and V, which comprises withdrawing a portion of ferrite-containing catalyst particles circulating in a fluid catalytic cracking apparatus, separating the thus withdrawn catalyst particles into metals-richly deposited catalyst particles and metals-poorly deposited ones by using a magnetic separator and then returning the metals-poorly deposited catalyst particles, together with fresh ferrite-containing catalyst particles, into said cracking apparatus.

Description: This invention relates to the fluid catalytic cracking of heavy fraction oils to obtain therefrom light fraction oils such as gasoline and kerosene. More particularly, it relates to such a process which comprises catalytically cracking, in the presence of a particulate iron oxide (ferrite)-containing catalyst, heavy fraction oils containing 0.5 ppm or more in total of at least nickel and vanadium. In conventional catalytic cracking, petroleum-derived hydrocarbons are contacted with a catalyst for cracking thereby to obtain a large quantity of light oil fractions such as LPG and gasoline as well as a small quantity of a cracked light oil, with coke deposited on the catalyst being burnt with air for removal thereof to enable the thus treated catalyst to be recycled for reuse. As starting oils in this case, there have heretofore been mainly used so-called distillates such as light gas oil (LGO) and heavy gas oil (HGO) from an atmospheric-pressure distilling column and vacuum gas oil (VGO) from a reduced-pressure distilling column. However, due to the recent worldwide need to use heavier crude oils and due to changes in demand for petroleum products in, for example, Japan, there has been a tendency to overproduce heavy oils. This has been appreciated from the twin standpoints of demand and supply of the petroleum products. Therefore, it has been necessary for heavy fraction oils including distillation residues to be used as starting oils in a catalytic cracking process. It is known, however, that heavy fraction oils, including distillation residues, contain metals such as nickel, vanadium, iron, copper and sodium in a far greater total amount than distillates, and that these metals will be deposited on a catalyst thereby hindering the activity and selectivity of the catalyst when the catalyst is used in catalytic cracking. In other words, the cracking rate will gradually decrease as the metals accumulate on the catalyst thereby making it substantially impossible to attain a desired cracking rate, while the amount of hydrogen evolved and the amount of coke produced will increase remarkably thereby making it difficult to operate equipment for carrying out the cracking. Further, at the same time, desired liquid products will be obtained in a decreased yield. Among said metals, particularly vanadium will destroy zeolite which is the active component of the catalyst and thereby lower the catalytic activity of the catalyst. Nickel does not decrease catalytic activity like vanadium does, but it will remarkably increase hydrogen and carbon due to its dehydrogenating catalytic activity. To relieve such effects of the contaminating metals on the catalyst in the system, there has usually been employed a process which comprises withdrawing periodically or continuously a portion of the particulate equilibrated catalyst present in the system and replenishing the system with an amount of fresh particulate catalyst, so as to maintain the activity of the equilibrium catalyst. In this case, it is necessary that the particulate catalyst be withdrawn in a remarkably large amount, this being very economically disadvantageous and being a serious problem particularly in the case of the fluid catalytic cracking of a residual oil containing metals in a large amount. Known measures which have been investigated for solving this problem include, on the one hand, removing metals deposited on catalysts and, on the other hand, inhibiting the activity of the metals. For example, in the first case there has been proposed a method for chemically treating the withdrawn equilibrium catalyst to remove the heavy metals therefrom and enable the thus treated catalyst to be re-used (F.J. Elvin et al, NPRA Annual Meeting, AM-86-41). Such a method will inevitably lead to discharge of a large amount of waste liquid whose disposal is very expensive if environmental pollution is to be prevented. From the point cf view of inhibiting the activity of the metals, known are a method which comprises adding a metal scavenger to the catalyst and a method which comprises adding to a starting oil a metal passivator such as antimony (U.S. Patents Nos. 3,711,422 and 4,025,458) or bismuth (U.S. Patents Nos. 4,083,807 and 3,977,963). In addition, it is known that alkaline earth metal compounds are effective as metal passivators (for example, Japanese Pat. Appln. Laid-Open Gazettes Nos. Sho 61-204041, Sho 60-71041, Sho 61-278351 and Sho 63-123804). Even with these methods, it has not been possible to fully prevent the contaminating metals from exerting their effects. Accordingly, in order to maintain the activity of the catalyst, the equilibrated catalyst needs to be partly withdrawn from the system and a supply of fresh catalyst made available for replenishing. When such catalyst exchange is effected, some of the catalyst particles withdrawn still have high catalytic activity. Thus, it follows that said catalyst exchange method uses the catalyst inefficiently. The present inventors of this application have already found that a portion of a particulate equilibrated catalyst on which the heavy metals are deposited which is withdrawn from the system may be separated by the use of a high gradient magnetic separator into one catalyst portion cn which more metals are deposited and another catalyst portion on which less metals are deposited and the less metals-deposited catalyst portion is then recycled to the system, whereby the activity of the equilibrated catalyst is enhanced and tlle selectivity thereof is remarkably improved (Japanese Patent Gazettes Nos. 63-37156 and 63-37835). This technique disclosed in said Gazettes is not in conflict with anti-metal measures such as the above-mentioned chemical treatment, metal scavengers and metal passivators and can be used jointly therewith. In such a method which comprises separating the equilibrated catalyst by the use of a magnetic separator into a mcre metal deposited portion and a less metal deposited portion, it is important to effect such separation precisely in accordance with the concentrations of metals deposited on the particulate catalyst, and the separation can be achieved more effectively using the difference in magnetizability (magnetic susceptibility) between the more metal deposited catalyst particles (greater magnetizability) and the less metal deposited ones less magnetizability). An object of this invention is to provide a fluid catalytic cracking process which comprises catalytically cracking heavy fraction oils containing a large amount of heavy metals such as nickel and vanadium while reducing decrease in catalytic activity of the catalyst due to the presence of the heavy metals. The present inventors made intensive studies mainly into improving the separability of catalyst particles into more metal deposited particles and less metal deposited ones by the use of a magnetic separator in a combination of fluid catalytic cracking of heavy fraction oils with magnetic separation of the above catalyst particles, and as the result of their studies they found that the object may be achieved by the use of a specified catalyst. This invention is based on the above finding. According to the present invention, there is provided a continuously operating process for the fluid catalytic cracking of a heavy fraction oil containing nickel and vanadium in a total amount of at least 0.5 ppm in a fluid catalytic cracking apparatus provided with a reaction zone, a stripping zone and a regenerating zone, which comprises the steps of (i) continuously feeding the heavy fraction oil to the cracking apparatus to undergo contact with particulate ferrite-containing catalyst particles in the reaction zone, the particulate ferrite having a saturation magnetization of not more than 10 emu/g before being introduced into the fluid catalytic cracking apparatus, thereby to crack the heavy fraction oils whereby a hydrocarbon mixture of lighter hydrocarbon oils and unreacted heavy fraction oils is obtained; (ii) separating the catalyst particles to which carbonaceous substances and a part of the hydrocarbon mixture are attached, from the remaining greater part of the hydrocarbon mixture, in the stripping zone; (iii) subjecting the catalyst particles thus separated to oxidizing treatment in the regenerating zone to decrease the content of carbonaceous substances and the hydrocarbon mixture attached to the catalyst particles, thereby to obtain regenerated catalyst particles; (iv) continuously recycling the regenerated catalyst particles thus obtained into the reaction zone; (v) withdrawing a portion of the particulate ferrite-containing catalyst particles flowing circulatively in the fluid catalytic cracking apparatus; (vi) separating said portion of the catalyst particles so withdrawn into magnetically attachable catalyst particles and magnetically unattachable catalyst particles by the use of a magnetic separator; and then (vii) returning the magnetically unattachable catalyst particles, together with fresh particulate ferrite-containing catalyst particles in which the particulate ferrite has a saturation magnetization of not more than 10 emu/g, into said cracking apparatus. This invention will be explained hereunder in more detail. The heavy fraction oils used herein are typically hydrocarbon oils which contain at least 5 vol.% of fractions boiling at 565°C or higher and have a density of at least 0.8 g/cm 3 at 15°C. The oils contain heavy metals such as iron, nickel, vanadium and copper, with nickel and vanadium being present in a total amount of at least 0.5 ppm. Such oils may be atmospheric-pressure distillation residues, reduced-pressure distillation residues, shale oils, tar sand bitumen, Orinoco tar, coal liquefied oils, and heavy fraction oils obtained by the hydrofining of such other oils. They may further include contents of comparatively light fraction oils (such as straight-run light oils, reduced-pressure light oils, desulfurized light oils and desulfurized reduced-pressure light oils). This invention is preferably applied to cracking of atmospheric-pressure distillation residues and reduced-pressure distillation residues. In cases where heavy fraction oils containing nickel and vanadium in a total amount of at least 2 ppm, more particularly at least 5 ppm, are used as the starting oils in this invention, then the cracking process of this invention will exhibit particularly great economic merits. The catalyst used in this invention usually comprises zeolite which is an active component and a matrix which supports the zeolite. The matrix carries ferrite particles having a saturation magnetization of not more than 10 emu/g, preferably 1-4 emu/g, dispersed therein. When the heavy fraction oils are subjected to fluid catalytic cracking using such a ferrite-containing catalyst, nickel contained in the heavy fraction oils will precipitate on the catalyst where the ferrite particles react with the precipitated nickel to produce nickel ferrite particles having a saturation magnetization of over 10 emu/g. Accordingly, once ferrite particles have a saturation magnetization of more than 10 emu/g, the difference in saturation magnetization between the ferrite particles and the nickel ferrite particles becomes small with the selectivity of metal deposited catalysts in magnetic separation becoming undesirably worsened. The ferrite of the fresh particulate-containing catalyst particles may be illustrated by zinc ferrite. Such particles usually have an average particle size of preferably 0.001-20 µm, more preferably 0.01-5 µm. In addition, the content of the ferrite particles in the catalyst is preferably 0.01-10 wt.%, more preferably 0.1-5 wt.%. The zeolite contained as the active component in the catalyst used in this invention is a crystalline aluminosilicate and faujasite-type zeolite is preferably used and ultrastable Y-type zeolite is particularly preferably used. The content of the zeolite in the catalyst is preferably 5-50 wt.%, more preferably 15-45 wt.%. The matrix which is the mother body supporting the above ferrite particles and zeolite is composed of a catalytically inert extender such as kaolin, and a binder such as alumina sol or silica sol; it may be incorporated with alumina, a metal scavenger and the like as required. It is preferable that the catalyst particles used in this invention have a bulk density of 0.5-1.0 g/ml, an average particle size of 50-90 µm, a surface area of 50-350 m 2 /g and a pore volume of 0.05-0.5 ml/g. The fluid catalytic cracking apparatus used in this invention is provided with a reaction zone, separation zone, stripping zone and catalyst regeneration zone, and it is usually operated at a reaction temperature of 480-550°C, a pressure of 1-3 kg/cm 2 G, a catalyst/oil ratio of 1-20 and a contact time of 1-10 seconds. The "fluid catalytic cracking" defined herein means that the heavy fraction oils (feed oils) are continuously contacted with the catalyst particles kept fluidized therewith under the above operational conditions thereby to crack said heavy fraction oils into lighter hydrocarbon oils such as LPG, gasoline, kerosene and light oil. Said contact may be effected either within fluid beds of the catalyst or in risers through which both the catalyst particles and feed oils flow upward for so-called riser cracking. A mixture of products and unreacted substances produced by the catalytic cracking, with the catalyst particles, is passed to the stripping zone where the greater part of the hydrocarbons such as the products and unreacted substances are removed from the catalyst particles. The catalyst particles to which the carbonaceous substances and a part of the heavy hydrocarbons are attached are passed from the stripping zone to the regeneration zone (regenerating tower) where they are subjected to oxidizing treatment to decrease the amount of the carbonaceous substances and hydrocarbons deposited thereon, thereby to obtain regenerated catalyst particles. These regenerated catalyst particles are continuously recycled to the reaction zone. In the fluid catalytic cracking process of this invention, the catalyst particles circulated from the reaction zone to the regeneration zone (such circulating catalyst being sometimes called "equilibrated catalyst" herein) are partly withdrawn through the stripping zone outlet, the regenerating zone outlet or other suitable outlets whose use does not interfere with the operation of the apparatus used in this invention. In this case, the withdrawal of a part of the equilibrated catalyst may be effected continuously or discontinuously at such fixed intervals as to exert no adverse effects on the resulting products. The catalyst so withdrawn may be subjected directly to magnetic separation using a magnetic separator or may be subjected to some suitable treatment before the magnetic separation. The magnetic separator used herein is preferably a high gradient magnetic separator having a magnetic field gradient of at least 200 gauss/cm, more preferably 2000x10 3 -20000x10 3 gauss/cm. The high gradient magnetic separator is designed such that a ferromagnetic packing material is placed within a uniform highly magnetic field space to constitute a high magnetic field gradient such as stated above around said packing material, such that ferromagnetic or paramagnetic particles are magnetically attached to the surface of said magnetic substance, and such that weakly magnetic or diamagnetic particles can be separated as magnetically unattached particles. The ferromagnetic packing material used herein is exemplified by a ferromagnetic fine wire assembly such as steel wool or steel net composed of fine wires having a diameter usually of 1-1000 µm. The high gradient magnetic separator is exemplified by that manufactured and sold by SALA Company, Sweden. Methods for treating solid fine particles by the use of a magnetic separator include a dry method which comprises using, as a carrier fluid, any one of air, nitrogen, steam and a mixture thereof and a wet method which comprises using, as a carrier fluid, any one of water and other liquids. Either the dry method or the wet method may be used in the practice of this invention. The process variables in the operation of the magnetic separator usually include magnetic field intensity, magnetic field gradient, linear velocity, concentration of particles, and treating temperature, and they will widely vary in their optimum value depending on the particle size of catalyst, the kind, condition and amount of metals deposited, the particle size and amount of iron oxide particles contained in the catalyst, the level of separation intended, and the selectivity of separation. The magnetic field strength is the intensity of magnetic field within the space in which said magnetic packing material is placed, and a magnetic field intensity of at least 200 gauss, preferably 1000-20000 gauss or more, is preferably used in both the dry method and the wet method. The magnetic field gradient is the change in amount of magnetic field intensity produced around said packing material with distance within the magnetic field. This variation can be effected by changing the intensity of magnetic field or the kind and diameter of said packing material, and the magnetic field gradient used in both the dry and wet methods is preferably at least 200 gauss/cm, more preferably 2000x10 3 -20000x10 3 gauss/cm. The expression "concentration of particles" is used herein to mean the catalyst particles which are to be magnetically separated in a gaseous or liquid carrier fluid, and a suitable concentration of catalyst particles is usually 0.01-100 g/l in the dry method and usually 0.01-1000 g/l in the wet method. The treating temperature refers to the temperature of catalyst particles which are to be subjected to magnetic separation, and, strictly speaking, it refers to the temperature of iron, nickel, vanadium or copper which is deposited on the catalyst particles. The treating temperature used is preferably not higher than the respective curie temperatures of these metals and is usually ambient temperature. It is possible to widely change the level of separation and the selectivity of separation by changing the linear velocity of the fluid passing through the magnetic field, and the linear velocity is increased when high selectivity is required. The linear velocity used is usually 0.01-100 m/sec in the dry method, and is usually 0.01-10000 m/hr in the wet method. The magnetic separator may be cut-in on the line of the fluid catalytic cracking apparatus or may be used batchwise without being so cut in. The catalyst particles (equilibrated catalyst) withdrawn are separated by the magnetic separator into metal-rich catalyst particles (magnetically attachable catalyst particles) on which iron, nickel, vanadium and copper are deposited in large amounts, and metal-poor catalyst particles (magnetically unattachable catalyst particles) on which such metals are deposited in comparatively small amounts. The weight ratio between the metal-rich catalyst particles and the metal-poor ones so separated is usually in the range of from 1: 100 to 100: 1, in some cases from 1: 1000 to 1000:1, and preferably from 1:10 to 10:1. The amount of metal deposited on the metal-rich catalyst particles will greatly vary depending on the amount of catalyst used, the properties of feed oils used, the reaction conditions and the like in the fluid catalytic cracking reaction, and is preferably at least 0.05 wt.%, more preferably 0.05-20 wt.% and most preferably 0.1-5 wt.%, as nickel equivalent. The "nickel equivalent" defined herein is a value represented by the following formula Ni equivalent = [Ni] + 0.25 x [V] wherein [Ni] and [V] are the concentrations of nickel and vanadium, respectively. The metal-poor catalyst particles separated still have high activity and, therefore, they are returned to the circulating system for recycle. It is customary in this case to maintain the amount of catalyst at a desired level while preventing the activity of the catalyst from decreasing in the circulating system by replenishing with fresh or regenerated catalyst in an amount equal to or more than that of the separated and removed metal-rich catalyst. Provided for through-charging of catalyst into the circulating system, is, for example, a regenerating tower inlet, a regenerating tower outlet transfer line or other arrangement which has little effect on the heat balance and fluidity balance in the system. The metal-rich catalyst particles separated and removed may be disposed of or may be subjected to ion exchange, chlorination, sulfurization, carbonylation, oxidation, reduction or the like thereby to detach the deposited metals from the catalyst particles for reuse thereof. The regeneration device for such catalyst regeneration may be connected to the magnetic separator to be cut-in on the line for the cracking. Alternatively, it may be operated batchwise without being so cut-in. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made by way of illustration only, to the accompanying drawings, wherein: Fig. 1 is a graph showing the relationship between the number of days for oil circulation and the amount of metals deposited in case of Example 2 and Comparative Example 2; Fig. 2. is a graph showing the relationship between the number of days for oil circulation and 221°C conversion; and Fig. 3. is a graph showing thc relationship between the number of days for oil circulation and the ratio (CN/CM) of the Ni concentration (CN) of the metal-poor catalyst particles to the Ni concentration (C51) of the metal-rich catalyst particles. This invention will be better understood by the following non-limiting Examples and Comparative Examples. Example 1 2155g of a diluted solution (SiO 2 concentration, 11.6%) of water glass, JIS No.3 were added dropwise to 337g of 40% sulfuric acid to obtain silica sol having a pH value of 3.0. Incorporated in the silica sol obtained were 350g of ultrastable Y-type zeolite (lattice constant 2.450 nm, tradename TSZ-330 HSA produced by Toso Co., Ltd., Japan), 390g of kaolin and 10g of zinc ferrite (average particle size: 2.2 µm) having a ferromagnetization of 1.8 emu/g, and the mixture obtained was kneaded and then spray dried by heated air at 250°C. The thus obtained spray dried product was washed with 5 liter of 0.2% ammonium sulfate at 50°C, thereafter dried in an ovell at 110°C and then further calcined at 600°C to obtain a catalyst (A). Then 1.0 wt.% of nickel was applied to the catalyst (A) according to Mitchell's method (Ind. Eng. Chem., Prod. Res. Dev., 19, 209 (1980)). More particularly, the catalyst (A) was impregnated with a solution of nickel naphthenate in toluene, after which the solvent was evaporated and the resulting solvent free catalyst was then calcined in air at 550°C for 3 hours, followed by being subjected to steaming at 800°C for 6 hours. In addition, a catalyst which was the same as the catalyst(A) but did not carry nickel was likewise subjected to steaming at 800°C for 6 hours. The magnetizability of each catalyst so obtained was determined by the following formula using a magnetic balance (tradename: magnetic balance NB-2 produced by Shimazu Seisakusho Co., Ltd., Japan). The results are as shown in Table 1. F = m.χ. dH dx F: magnetic force(dyn), m: mass (g) χ: magnetizability (emu/g), H:magnetic field intensity(Oe) dH / dx : magnetic field gradient (Oe/cm) Comparative Example 1 A commercially available catalyst (Octacat produced by W.R. Grace Company) was made to carry 1.0 wt. % nickel therein in the same manner as in Example 1. The nickel-carrying catalyst so obtained and a nickel-free catalyst which was the same as the above commercially available catalyst were each subjected to steaming at 800°C for 6 hours and then measured for their magnetizability in the same manner as in Example 1. The results are as shown in Table 1. Catalyst Catalyst (A) Commercially available catalyst (Octacat) Nickel (wt. %) 0 1 0 1 Magnetizability (10 -6 emu/g) 6.4 10.3 6.4 10.3 0.4 1.4 Example 2 Using a scaled-up apparatus for producing a catalyst, 100kg of catalyst(A) were produced in the same manner as in Example 1. The catalyst(A) was evaluated using a riser-type FCC pilot plant. The scale of the plant was expressed as an inventory of 40 kg (of catalyst) and a feed of 1 bbl/D, and the plant was operated at a reaction temperature of 520°C, a catalyst/oil ratio of 8 and a regenerating tower temperature of 700-710°C. The feed oils were a mixture of 50 wt.% of Taching (Taihei) atmospheric-pressure residual oils with 50 wt.% of desulfurized HVGO, and a metal naphthenate was injected into the feed to accelerate the deposition of metals on the catalyst particles. The amount of metal naphthenate injected was 85 ppm of Ni and 8.5 ppm of V based on the feed. Before the catalyst(A) was charged into the apparatus, it had been subjected to steaming with 100% steam at 800°C for 6 hours in order to pseudo-equilibrate the catalyst. The fluid catalytic cracking operation was so operated for 20 days under the above conditions and additional conditions that the makeup of fresh catalyst was 0.4 kg/D, the makeup of pseudo-equilibrated catalyst was 3.8 kg/D, the loss of catalyst was 0.8 kg/D and the amount of equilibrated catalyst withdrawn was 3.4 kg/D. Thereafter, the operation of the cracking apparatus was combined with that of a magnetic separator for an additional 20 days. After the combination with the magnetic separator, the makeups or replenishments of the fresh catalyst and pseudo-equilibrated catalyst, as well as the loss of catalyst, were the same as before said combination. In addition, while the cracking apparatus was combined with the magnetic separator, 16 kg/D of the equilibrated catalyst particles zere treated in the magnetic separator to separate them into 3.4kg/D of metal-rich (magnetically attachable) catalyst particles and 12.6 kg/D of metal-poor (magnetically unattachable) ones, after which the former (metal-rich) particles were disposed of and the latter (metal-poor) particles were returned to the apparatus. At this time, the magnetic separator was operated under the conditions of a magnetic field intensity of 13 KG, a carrier air velocity of 1.7 m/s, a particle concentration of 0.5g/l and the treating temperature being ambient temperature. Figs. 1-3 indicate "amounts of metals deposited on equilibrated catalyst", "221°C conversion" and "ratio (CN/CM) between Ni concentration of magnetically unattachable catalyst particles (CN) and Ni concentration of magnetically attachable ones (CM)", versus "oil circulation time period", respectively. Further, Table 2 indicates data for 20 days' oil circulation (without combination with magnetic separator) and data for 40 days' oil circulation (in combination with magnetic separator). Comparative Example 2 The commercially available catalyst (OCTACAT) was evaluated in the same manner as in Example 2 using the aforesaid pilot plant. The results are as indicated in Figs. 1-3 and Table 2. Catalyst (A) Commercially available catalyst (OCTACAT) Days for oil circulation 20 40 20 40 Magnetic separation Non-combination Combination Non-combination Combination Amount of metals deposited (ppm) 3200 2400 3150 2730 221°C Conversion (vol.%) 75.0 77.7 75.3 76.2 Gasoline yield (vol.%) 58.1 59.7 58.1 58.7 Hydrogen yield (wt.%) 0.31 0.27 0.34 0.31 Coke yield (wt.%) 6.01 5.89 6.26 6.17 As is seen from the foregoing results, the catalyst (A) containing ferrite particles exhibited a greater increase in magnetizability and better separability by the magnetic separator than the commercially available catalyst when nickel was deposited on each of the catalysts. When the same makeup or replenishment of fresh catalyst was effected, the amount of metals deposited on the catalyst subsequent to the combination with the magnetic separator was less in cases where the catalyst (A) was used and, consequently, the use of the catalyst (A) increased the conversion rate and gasoline yield while decreasing hydrogen and coke yields. In addition, as previously mentioned, the process of this invention is advantageous over conventional processes in that it is not necessary to withdraw such a remarkably large amount of the circulating (equilibrated) catalyst particles as in the conventional processes for replenishing fresh catalyst particles. It therefore eliminates wasteful disposed of still somewhat effective catalyst particles and there is absence of expenditure for disposing of waste liquids which raise environmental pollution levels. This is because there is no chemical treatment of the metal-deposited catalyst in liquid phase to remove the metals from the catalyst. The process of this invention is overall, simple to operate. In summary, the process of this invention in which particulate ferrite-containing catalyst is used makes it possible to enhance efficiency and selectivity of magnetic separation, and to maintain the activity and selectivity of the equilibrated catalyst at a high level.

Claims: A continuously operating process for the fluid catalytic cracking of a heavy fraction oil containing nickel and vanadium in a total amount of at least 0.5 ppm in a fluid catalytic cracking apparatus provided with a reaction zone, a stripping zone and a regenerating zone, which comprises the steps of (i) continuously feeding the heavy fraction oil to the cracking apparatus to undergo contact with particulate ferrite-containing catalyst particles in the reaction zone, the particulate ferrite having a saturation magnetization of not more than 10 emu/g before being introduced into the fluid catalytic cracking apparatus, thereby to crack the heavy fraction oils whereby a hydrocarbon mixture of lighter hydrocarbon oils and unreacted heavy fraction oils is obtained; (ii) separating the catalyst particles to which carbonaceous substances and a part of the hydrocarbon mixture are attached, from the remaining greater part of the hydrocarbon mixture, in the stripping zone; (iii) subjecting the catalyst particles thus separated to oxidizing treatment in the regenerating zone to decrease the content of carbonaceous substances and the hydrocarbon mixture attached to the catalyst particles, thereby to obtain regenerated catalyst particles; (iv) continuously recycling the regenerated catalyst particles thus obtained into the reaction zone; (v) withdrawing a portion of the particulate ferrite-containing catalyst particles flowing circulatively in the fluid catalytic cracking apparatus; (vi) separating said portion of the catalyst particles so withdrawn into magnetically attachable catalyst particles and magnetically unattachable catalyst particles by the use of a magnetic separator; and (vii) returning the magnetically unattachable catalyst particles, together with fresh particulate ferrite-containing catalyst particles in which the particulate ferrite has a saturation magnetization of not more than 10 emu/g, into said cracking apparatus. A process according to claim 1, wherein the particulate ferrite has a saturation magnetization of 1 to 4 emu/g before being introduced into the fluid catalytic cracking apparatus. A process according to claim 1 or 2, wherein the ferrite of the fresh particulate ferrite-containing catalyst particles is zinc ferrite. A process according to claim 1, 2 or 3, wherein the catalyst particles contain the particulate ferrite in an amount of 0.01 - 10% by weight. A process according to any one of claims 1 to 4, wherein the magnetically attachable catalyst particles contain particulate nickel ferrite having a saturation magnetization of over 10 emu/g, said particulate nickel ferrite having been produced by reaction of the particulate ferrite with nickel precipitated on the particulate ferrite-containing catalyst particles. A process according to any one of claims 1 to 5, wherein the magnetically attachable catalyst particles are those catalyst particles on which nickel and vanadium have been deposited in an amount of at least 0.05% by weight as nickel equivalent, the nickel equivalent being a value represented by the following formula Ni equivalent = [Ni] + 0.25 x [V] wherein [Ni] and [V] are the concentrations of nickel and vanadium, respectively. A process according to any one of claims 1 to 6, wherein the catalyst particles have a bulk density of 0.5 - 1.0 g/ml, an average particle size of 50 - 90 µm, a surface area of 50 - 350 m 2 /g and a pore volume of 0.05 - 0.5 ml/g. A process according to any one of claims 1 to 7, wherein the fluid catalytic cracking apparatus is operated at a reaction temperature of 480 - 550°C, a pressure of 1 - 3 kg/cm 2 G, a catalyst/oil ratio of 1 - 20 and a contact time of 1 - 10 seconds.

Inventors: INO TAKASHI, KATO KOICHI, NAKATSUKA YASUO, INO, TAKASHI, KATO, KOICHI, NAKATSUKA, YASUO, INO, TAKASHI, C/O NIPPON OIL CO., LTD., KATO, KOICHI, C/O NIPPON OIL CO., LTD., NAKATSUKA, YASUO, C/O NIPPON OIL CO., LTD.
Applicants: NIPPON OIL CO LTD, NIPPON OIL COMPANY, LIMITED
Application year: 1994
Main classification: C10G11
IPC codes: C10G11